1. Field of the Invention
The present invention relates to a liquid transfusion apparatus adapted to forcibly transfusing a transfusion liquid by a pressure generated by a pump or the like.
2. Description of the Related Art
In general, a liquid transfusion apparatus which forcibly feeds a transfusion liquid by a pressure offers advantages over gravity type of liquid transfusion apparatus, such as greater degree of freedom of control of the flow rate of the liquid to be transfused, higher stability of the flow rate, and so forth. When this type of liquid transfusion apparatus is used for transfusion treatment, there is a risk that the pressure at which the transfusion liquid is supplied to the patient's body is dangerously changed due to, for example, inadequate prick of the needle, accidental removal of the needle from the blood vessel as a result of movement of the patient, bending of the transfusion tube, and so forth.
In order to avert from such a danger, the known liquid transfusion apparatus feeding forcibly the transfusion liquid is provided with means for monitoring the pressure of the transfusion liquid during the transfusion treatment. More specifically, the pressure of the transfusion liquid is detected by a pressure sensor disposed at an intermediate portion of the transfusion tube, and the pressure signal from the pressure sensor is converted into a digital signal by an A/D converter, and thus the converted signal is delivered to a display unit which digitally displays the pressure level corresponding to the digital signal. The pressure signal from the pressure sensor also is supplied to a comparator which compares the pressure level with a predetermined reference level When the reference level is exceeded by the pressure level, an alarm is sounded to inform that the pressure of the transfusion liquid is abnormally high.
In this known apparatus, the display unit displays the level of the pressure of the transfusion liquid in, for example, psi (pound square inch) as it is. Thus, there is no means which would show how much the pressure of the transfusion liquid is deviated from a normal pressure level, and how much a margin of pressure is left until the alarm is sounded. Thus, a doctor or a nurse has to determine the margin of pressure which is left until the alarm is sounded, by reading the level displayed on the display unit and comparing the read level with the normal pressure level or a pressure level at which the alarm is to be sounded. Namely, it has been impossible to determine, at a glance of the display unit, the deviation from the normal pressure level and the degree of margin of pressure which is left until the alarm is to be sounded, at a glance of the display unit. In addition, the allowable limit level of the pressure of the transfusion liquid varies according to the nature of the patient. Namely, the maximum allowable pressure for adults is different from that for infants. This means that the pressure level at which the alarm is to be sounded must be changed according to the type of the patient. Once the pressure level at which the alarm is to be sounded is changed, the doctor or the nurse is obliged to reconsider the degree of margin pressure which is left until the alarm is sounded. Thus, the known liquid transfusion apparatus cannot be used conveniently and, hence, an improvement has been required.